Permeability separation devices in which the separatory membrane takes the form of a large number of hollow fiber lengths are now well known. Such devices are coming into widespread use for dialysis, blood oxygenation, ultrafiltration, reverse osmosis, separation of geseous mixures and the like. While considerable ingenuity has been exercised in developing efficient manufacturing processes such devices are generally expensive and produced only at relatively low rates.
In the case of biomedical devices, even very low rates of blood loss or contamination with foreign matter is intolerable. Thus, hollow fiber devices having even one leak per twenty thousand fibers are not acceptable for medical use. Unfortunately, it is generally not practicable to detect leaks or flaws conductive to leaking in the fibers before they are potted and fitted into a test assembly or final device. Furthermore, hollow fibers of a permeability requisite to operations such as blood dialysis or oygenation are generally fragile. Consequently, leaks may develop during assembly of even flaw-free fibers. It is then apparent, in the interests of economy, conservation of materials and device availability that a method of salvaging leaky units is highly desirable.
An effective method must provide for certain and facile location of leaks and for closing them off selectively, i.e., without also closing off access to a substantial proportion of the good fibers in the same area. The problem is complicated by the fact that permeability retention frequently requires maintaining the fibers in a wet or fluid-swollen condition until the device is put into use. A further complication is that only medically acceptable materials may be incorporated into devices, such as kidney and lung units, from which treated blood is returned to patients.
Among the prior art of interest, U.S. Pat. No. 3,499,602 teaches a method for repairing leaks in a fluid separation device comprising a fluid-tight tubular casing closed at either end by cast wall members, i.e., tubesheets, and having a plurality of hollow filaments extending between the members. With the casing oriented vertically, a solidifiable liquid is placed on the upper face of a tubesheet and is drawn into any leaks in that tubesheet and into any filament having leaks, by application of a pressure differential across the filament walls. The surplus liquid is then withdrawn and the liquid in the filled filaments or tubesheet channels is solidified.